Impact of 2003-2015 forest cover changes on trees diversity in GISHWATI landscapes

Abstract

The deforestation of tropical forests has been considered as the major driver of the forest cover change and loss of about 50,000 plant and animal species is attributed to it. Two main interventions to be adopted to tackle the issue, are (i) the protection of the current forests, (ii) rehabilitate and restore of degraded forests. This study was carried out in Gishwati Landscapes located in North–West of Rwanda which include the former Gishwati Forest Reserve. The main objective of this study was to quantify forest cover change from 2003 to 2015 and compare current tree species diversity and their distribution in different forest structures (restored and remnant forests. Supervised classification was done in Erdas Imagine and Arc Map software in analysing L7-ETM+(2003) and L8 OLI/TIRS (2015) images to quantify land uses and forest cover changes. From land cover change detection results, two different types of forested areas were found: (i) undestroyed natural forest areas and (ii) regenerated forest from converted cropland and pasture in which 120 samplings plots were established and tree species were recorded. Further analysis was done using PAST for tree species diversity. Supervised classification gave three main land uses which are cropland, forest, and pasture. Change detection showed that cropland reduced in size by 25%, forest increased by 5.2 % and pasture by 20%. For tree diversity and species richness, the forest derived from cropland has high species richness (21), followed equally by forest to forest and pasture to forest (20). Species dominance index of the remnant forest is higher (0.1998), followed by pasture converted (0.1891) while the cropland converted to forest come at the last position (0.145). Simpson’s index of forest derived from cropland was higher (0.855), followed by pasture derived (0.8109) and finally by the remnant forest (0.8002) while the Species evenness is higher in the forest from cropland (0.4457) followed by forest converted from pasture (0.3995) and then remnant forest (0.3585). There has been a positive forest cover from 2003 to 2015 which is beneficial for the sustainability of biodiversity. Good news is that it has been observed that conversion from cropland to forest can increase up forest cover than converting pasture to forest. Remnant forest is more abundant in trees than restored forest which still emphasize role of forest protection before rehabilitation and restoration.

iv Key words Key words: Gishwati, land use, forest cover change, species richness, tree diversity.